File:Hand-book of physiology (1892) (14578809439).jpg

Identifier: handbookofphysio00bake (find matches)
Title: Hand-book of physiology
Year: 1892 (1890s)
Authors: Baker, W. Morrant, (William Morrant), 1839-1896 Harris, Vincent Dormer Kirkes, William Senhouse, 1823-1864. Hand-book of physiology. 13th ed
Subjects: Physiology Human physiology
Publisher: London : John Murray
Contributing Library: Francis A. Countway Library of Medicine
Digitizing Sponsor: Open Knowledge Commons and Harvard Medical School

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ecome differentiated into three parts :(a) the epithelium lining the central canal; (b) the grey matter;(c) the external white matter. The last is derived from the outer-most part of the epiblastic walls by the conversion of the cellsinto longitudinal nerve-fibres. The fibres being without anymyelin sheath, are for a time grey in appearance. The whitematter corresponds in position to the anterior and posteriornerve-roots, and are the anterior and posterior white columns CH. XIX.) THE BKAIN. 833 It is at first a very thin layer, but increases in thicknessuntil it covers the whole cord. The grey matter too arises fromthe cells by their being prolonged into fibres. The change in thecentral cells is sufficiently obvious. The anterior and posteriorcornua of grey matter and the anterior grey commissure thenappear. The anterior fissure is formed on the fifth day by thegrowth downwards of the anterior cornua of grey matter towardsthe middle line. The posterior fissure is formed later. The h 4
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Fig. 502.—Early stages in development of human brain (magnified). 1, 2, 3, are from anembryo about seven weeks old ; 4, about three months old. m, middle cerebral vesicle(mesencephalon); c, cerebellum; ra 0, medulla oblongata; i, thalamencephalon; /;,hemispheres; i, infundibulum; Fig. 3 shows the several curves which occur in thecourse of development; Fig. 4 is a lateral view, showing the great enlargement of thecerebral hemispheres which have covered in the thalami, leaving the optic lobes, in,uncovered. (Kolliker.) N.B.—In fig. 2 the line i terminates in the right hemisphere; it ought to be continuedinto the thalamencephalon. whole cord now becomes circular. The posterior grey commissureis then formed. When it first appears, the spinal cord occupies the whole lengthof the medullary canal, but as development proceeds, the spinalcolumn grows more rapidly than the contained cord, so that thelatter appears as if drawn up till, at birth, it is opposite the thirdlumbar vertebra, and i

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